The present invention relates to a process for the preparation of a monoallylamine polymer aqueous solution as well as a high-molecular-weight monoallylamine polymer aqueous solution. More specifically, the present invention relates to a process for preparing a high-molecular-weight monoallylamine polymer aqueous solution efficiently and industrially advantageously, and a high-molecular-weight monoallylamine polymer aqueous solution which is not only useful in various fields including polymer flocculants and coating agents but also useful as a raw material for water-absorbing resins and ion-exchange resins and a raw material for functional polymer materials.
A monoallylamine polymer is a linear olefin polymer having a primary amino group in a side chain, and it is a cationic polymer compound which is well soluble in water and positively charged in water. Such a monoallylamine polymer has a characteristic reactive polymer structure and characteristic properties, so that it is used in many fields including polymer flocculants, coating agents, dye fixing agents for reactive dyes and direct dyes and additives for inkjet recording papers.
While it is generally known that a monoallylamine does not easily undergo polymerization due to its degradative chain transfer, various methods have been proposed for preparing a monoallylamine addition salt polymer or a free monoallylamine polymer by polymerizing a monoallylamine addition salt in the presence of a specific radical polymerization initiator.
However, these methods involve various problems when a high-molecular-weight and free monoallylamine polymer is prepared, and these methods have not been fully satisfactory.
For example, JP-A-58-201811 describes that a monoallylamine phosphate aqueous solution is polymerized in the presence of a radical polymerization initiator having a molecule containing an azo group and a cationic nitrogen, whereby a monoallylamine phosphate polymer having a number average molecular weight of 36,000 to 45,000 can be obtained. It is thinkable to produce a high-molecular-weight and free monoallylamine polymer by preparing a high-molecular-weight monoallylamine phosphate polymer according to the above method and then neutralizing the monoallylamine phosphate polymer with an alkali.
However, this method involves a problem in the removal of phosphate formed as a byproduct. An inorganic phosphate cannot be removed by electrodialysis using an ion-exchange membrane. It is therefore thinkable to remove the inorganic phosphate by neutralizing a polymerization-completed solution and filtering off the precipitated phosphate. When this method is actually attempted, however, there are problems that the removal of the inorganic phosphate is insufficient, and that a free monoallylamine polymer adheres to the inorganic phosphate that is filtered off, so that the yield of the polymer as an end product is decreased. Further, phosphate that is inevitably contained in the polymer is not necessarily desirable in view of environments.
JP-A-10-330427 discloses a method of producing a high-molecular-weight monoallylamine hydrochloride polymer by polymerizing a monoallylamine hydrochloride aqueous solution in the presence of the above radical polymerization initiator and a specific crosslinking agent. However, this method has a problem that the monoallylamine hydrochloride polymer inevitably contains units derived from the crosslinking agent.
Further, JP-B-6-2779 discloses a method in which a monoallylamine inorganic acid salt aqueous solution is polymerized in the presence of a specific radical polymerization initiator having a molecule containing an azo group and an allylamidino group, to produce a high-molecular-weight monoallylamine inorganic acid salt polymer. In this method, however, the high-molecular-weight polymer is obtained by using a large amount of a catalyst, so that it is considered that the allylamidino group is taken into the polymer. Presumably for this reason, there is a problem that the molecular weight of the polymer decreases in the aqueous solution with the passage of time. This phenomenon is presumably caused by the decomposition of the amidino group in the polymer.
Concerning the polymerization of a monoallylamine sulfate, for example, JP-B-62-31722 discloses a method in which an aqueous solution of monoallylamine sulfate is polymerized in the presence of a radical polymerization initiator having a molecule containing an azo group and cationic nitrogen, then a polymerization-completed solution and water are mixed to form a precipitate in the form of a starch syrup, the precipitate is purified to obtain a solid of a monoallylamine sulfate polymer and the solid of a monoallylamine sulfate polymer is treated with ammonia-methanol to obtain a methanolic solution of a monoallylamine polymer.
In this method, however, handling of the precipitate in the form of a starch syrup is complicated when the monoallylamine sulfate polymer is purified, and it is difficult to industrially produce a free monoallylamine polymer.
Further, JP-A-58-201811 discloses a method in which an aqueous solution of a monoallylamine sulfate is polymerized in the presence of a radical polymerization initiator having a molecule containing an azo group and cationic nitrogen, a polymerization-completed solution and water are mixed to form a precipitate in the form a starch syrup, the precipiate is fully washed and then dissolved in concentrated hydrochloric acid, and the resultant solution is added to methanol to re-precipitate a solid, whereby a monoallylamine hydrochloride polymer having a number average molecular weight of 6,500 is produced.
However, this method has a problem that it is difficult to wash the above precipitate since the handling of the precipitated monoallylamine sulfate polymer in the form of a starch syrup is troublesome. According to studies made by the present inventors, a polymer finally obtained is not completed as a product of a hydrochloride, which presumably results in the polymer therefore having a low number average molecular weight of 6,500.
Under the circumstances, it is therefore a first object of the present invention to provide an industrially advantageous process capable of efficiently producing a high-molecular-weight and free monoallylamine polymer aqueous solution from a monoallylamine as a raw material with easy purification without using a phosphate thereof.
It is a second object of the present invention to provide a high-molecular-weight monoallylamine polymer aqueous solution which is useful in various fields of polymer flocculants and coating agents, which does not contain any unit derived from a crosslinking agent or phosphorus and which is stable with the passage of time.
For achieving the above objects, the present inventors have made diligent studies and as a result have found the following. A monoallylamine sulfate is polymerized in an aqueous medium in the presence of a specific radical polymerization initiator and the polymerization solution is neutralized with an alkali, whereby, unexpectedly, a high-molecular-weight and free monoallylamine polymer aqueous solution can be easily obtained, and the above object can be achieved. On the basis of this finding, the present invention has been accordingly completed.
That is, the first object of the present invention is achieved by a process for the preparation of a monoallylamine polymer aqueous solution, which comprises polymerizing a monoallylamine sulfate in an aqueous medium in the presence of a radical polymerization initiator having a molecule containing an azo group and cationic nitrogen and neutralizing the resultant polymerization solution with an alkali, to obtain an aqueous solution containing a high-molecular-weight monoallylamine polymer having a weight average molecular weight, measured by a sedimentation equilibrium method, of 20,000 to 180,000.
Further, the second object of the present invention is achieved by a high-molecular-weight monoallylamine polymer aqueous solution containing neither a unit derived from a crosslinking agent nor phosphorus and containing a monoallylamine polymer having a weight average molecular weight, measured by a sedimentation equilibrium method, of 20,000 to 180,000.